Production of high quality blended jet fuels

ABSTRACT

A LOW SMOKE POINT (E.G., 29) JET FUEL CAN BE USED TO PRODUCE A HIGHER SMOKE POINT FUEL (E.G. 40+) BY BLENDING WITH AN ADDITIONAL MORE HIGHLY PARAFFINIC FUEL (E.G. HIGH IN C10-C12 NORMAL PARAFFINS) BOILING MAINLY WITHIN THE FUEL OIL BOILING RANGE (E.G. 10% POINT OF AT LEAST 270* F. AND 90% POINT LESS THAN 540*F.). A PREFERRED GROUP OF PARAFFINIC FUELS COMPRISES N-DECANE, N-DODECANE, HYDROGENATED BUTYLENE AND/OR PROPYLENE POLYMERS (E.G. TRIMER, TETRAMER) PREFERABLY HYDROGENATED PROPYLENE &#34;TETRAMER&#34; BOILING MAINLY ABOVE 350*F. (E.G. 10% POINT OF 360*F.). THE PREFERRED 29+ SMOKE POINT FUEL FOR BLENDING WITH N-DODECANE OR HYDROGENATED PROPYLENE TETRAMER IS OBTAINED BY A TWO STAGE HYDROGENATION OF A PARAFFINIC STRAIGHT RUN KEROSENE HAVING AN API GRAVITY OF AT LEAST 42, AND CONTAINING 12-16 WEIGHT PERCENT AROMATICS AND AT LEAST 45 WEIGHT PERCENT PARAFFINS. THE BLENDED FUEL ALSO CAN HAVE A DESIRABLY LOW FREEZE POINT THE N-PARAFFINS CAN ALSO BE OBTAINED BY MOLECULAR SIEVE SEPARATION FROM A KEROSENE FRACTION.

United States Patent Int. Cl. C101 1/04 US. Cl. 208-57 8 Claims ABSTRACTOF THE DISCLOSURE A low smoke point (e.g., 29) jet fuel can be used toproduce a higher smoke point fuel (e.g. 40+) by blending with anadditional more highly parafiinic fuel (e.g. high in C -C normalparafiins) boiling mainly within the fuel oil boiling range (e.g. 10%point of at least 270 F. and 90% point less than 540 F.). A preferredgroup of parafiinic fuels comprises n-decane, n-dodecane, hydrogenatedbutylene and/or propylene polymers (e.g. trimer, tetramer) preferablyhydrogenated propylene tetramer boiling mainly above 350 F. (e.g. 10%point of 360 F.). The preferred 29+ smoke point fuel for blending withn-dodecane or hydrogenated propylene tetramer is obtained by a two stagehydrogenation of a paraffinic straight run kerosene having an APIgravity of at least 42, and containing 12-16 weight percent aromaticsand at least 45 weight percent paraffins. The blended fuel also can havea desirably low freeze point. The n-parafiins can also be obtained bymolecular sieve separation from a kerosene fraction.

CROSS REFERENCES TO RELATED APPLICATIONS The present application is acontinuation-in-part of Ser. No. 799,499, filed Feb. 14, 1969 of MerritC. Kirk, Jr., entitled Producing High Quality Jet Fuels by Two StageHydrogenation, now US. 3,594,307 issued July 20, 1971. Other related,commonly owned applications are as follows:

Serial Filing Patent Issue numb er date number date The disclosure ofall of the above patents and applications is hereby incorporated hereinby reference.

SUMMARY OF THE INVENTION Jet fuels having high smoke points (e.g. atleast 35) and low freeze points (e.g. less than 20 F., typically lessthan 50 F.) can be obtained by blending a dearomatized straight runkerosene with a paraflin component such as n-decane, n-dodecane,hydrogenated propylene tetrarner and hydrogenated butylenetrimer.

This invention relates to the production of jet fuel (such as Mach 2JP-5 or JP-5A) and special fuels requiring a luminometer number above 75(e.g., 75-100) by hydrogenation of petroleum charges having a sufficientcontent of aromatic or olefinic hydrocarbons to cause them to have anASTM smoke point below 28 (typically below 25). Preferably, the olefinicor aromatic hydrocarbons in such charges must be such that they can beconverted by deep hydrogenation to materials boiling mainly within theboiling range specified for the desired jet fuel, or that the productstream containing the hydrogenation 3,788,971 Patented Jan. 29, 1974product of these aromatic hydrocarbons boils mainly within the rangespecified for the desired jet fuel. Also, the aromatic and/orolefin-containing stream, or the aromatics and/or olefins which arehydrogenated, should be capable of being converted, upon deephydrogenation, to a product having a smoke point of at least 29 (morepreferably, at least 35 Among the streams which are suitable feed stocks(or charges) for conversion to jet fuel by such a deep hydrogenationprocess are the heavy recycle from reforming of naphtha, straight-runkerosene, catalytic gas oil, straight chain C -C olefins (e.g.,propylene tetramer and/or pentamer, etc.), distillate from thermallycracked tar sands bitumen, distillate fractions of such feed stocks andblends of two or more such feed stocks (including blends of distillatefractions of such feed stocks). One preferred charge stock is astraight-run kerosene containing at least 9 weight percent of aromatics(e.g., 9l6%) and which boils mainly in the range of 400-500" F. Anothersuitable charge stock is the 400-500 F. fraction from the catalyticcracking of gas oils (including hydrocracking).

Also suitable is a charge comprising jet fuel range distillate (e.g.,boiling mainly in the range of 350550 F.) from coked bitumen separatedfrom tar sands (as by the hot water process). Typical of the prior arton such sep arations of bitumen from tar sands and further treatment toyield such distillates are US. Pat. No. 3,401,110 to Floyd et al. andPlant Starts, Athabasca Now Yielding Its Hydrocarbons in Oil and GasJournal, Oct. 23, 1967 by Bachman, W., and Stormont, D. For the firsthydrogenation stage of the present invention, such distillate fromthermally cracked bitumen is preferably reduced to less than 35 weightpercent olefins and aromatics by contact with a catalyst comprisingcobalt and/or nickel and molybdenum (most preferably in sulfide form)and with -95% pure hydrogen at 800 p.s.i. to 3000 p.s.i. (preferably1000-2000 p.s.i.g.), at 65'0-750 F., at a liquid hourly space velocityin the range of 0.25-2.5 (typically 0.75-1.25) at a gas recycle of atleast 3000 s.c.-f./ bbl. (typically 4000-8000). Such distillate can alsobe advantageously blended with at least one other of the previouslyreferred to charge stocks to produce a suitable charge for the two stagehydrogenation process of the present invention.

For all such charges, the desired deep hydrogenation can be effected bya two-stage catalytic hydrogenation process.

In the first stage, the petroleum charge stock is contacted withhydrogen (preferably 50-100% pure H typically 90%) and a catalyst,primarily in order to remove sulfur and nitrogen compounds (however,some saturation can also be effected in this stage). The preferredcatalyst will contain at least one member selected from the groupconsisting of nickel, cobalt, iron, molybdenum and tungsten and oxidesand sulfides thereof, preferably on an inert porous carrier. Conditionsinclude a temperature in the range of 500-785 F. (for example, 650-750F.) at a pressure of 350-3000 p.s.i.g. (for example, 500-1500 p.s.i.g.)with a liquid hourly space velocity of 0.5 to 10.0 (for example, 1.0 to6.0) and a hydrogen circulation rate of 0 to 20,000 standard cubic feetper barrel of charge stock (for example, 1,500-10,000 s.c.f./bbl.)

The product of this first hydrodesulfurization" or hydrorefining step isthen contacted in a second hydrogenation stage (preferably with 65-100%pure hydrogen) at temperatures from 450 F. to 775 F. (for example,450-700 F.) at a pressure of 500-3000 p.s.i.g. (for example, 500-1500p.s.i.g.), a liquid hourly space velocity of about 0.25 to 10.0 (e.g., 1to 10.0) and ahydrogen circulation rate of 0 to 20,000 (e.g.,2,000-10,000) s.c.f./ bbl. of the product of the first stage.

The combination of the conditions in each of the two hydrogenationstages is selected to produce a superior jet fuel having a luminometernumber of at least 75. Such a luminometer number is obtained when theASTM smoke point is at least 29 (and, with our preferred charge stocks,when the ASTM smoke point is at least 33, more preferably, at least 35).The art is familiar with a correlation developed by the CaliforniaResearch Corporation, whereby the luminocity number can be determinedfrom the ASTM smoke point, or vice versa. By this correlation, it hasbeen established that, for example, the maximum luminocity number whichcan be obtained from petroleum based fuel having a smoke point of 25 isabout 65 (and the minimum about 50). Similarly, the correlation showsthat to obtain a luminocity number of 75 from a petroleum fuel, the ASTMsmoke point must be at least 29, and may have to be as high as 35 (i.e.,32:3).

Conversely, for fuels having smoke points of 29, the luminocity can varyfrom about 62 to 75.

Preferred catalysts in the second hydrogenation stage are those whichcomprise a metal selected from the group consisting of nickel, cobalt,tungsten, molybdenum, Ru, Rh, Os, Ir and the noble metal hydrogenationcatalysts (e.g., Pt, Pd). Preferably, said catalyst is supported on aporous refractory support which does not have appreciable crackingactivity at the contact conditions (for example, alumina, kieselguhr,carbon, etc.). The second stage catalyst can also comprise sulfides (orsulfided oxides) of such metals when at least a trace (5-50 ppm.) ofsulfur (preferably as H 3 or organic sulfides) is maintained in thecharge to the second stage.

Generally, when the charge stock comprises acyclic C -C olefins, astraight-run kerosene, or a fraction derived from hydrocracking a gasoil (or from hydrocracking a heavy distillate from crude oil), orcomprises blends of at least two such charges, the resulting productfrom the second hydrogenation stage will have a luminometer number of atleast 75 when the product of the second hydrogenation stage containsless than 8 weight percent of aromatics and olefins. More preferably,the second stage product contains less than 4 percent (typically 0-2%)of aromatics and less than of olefins.

However, for any given charge stock, it is within the skill of the artto determine, by a series of experiments, the degree of hydrogenationwhich is necessary to produce a second stage product having the requiredluminometer number.

When the feed stock is highly aromatic, such as a nonhydrocrackedcatalytic gas oil, coked distillate from tar sands bitumen, or therecycle fraction from the reforming of naphtha, non-destructivehydrogenation alone (even in two stages) may not be suflicientprocessing to produce a jet fuel having a luminometer number of at least75. With such highly aromatic feed stocks (which upon deep hydrogenationconvert to products having a high content of naphthene hydrocarbons) itis frequently desirable to reduce the proportion of naphthenic carbonatoms to parafiinic carbon atoms in the final fuel. This can be effectedby the means taught in the above-referredto copending application, Ser.No. 781,095 and in its copending parent application which matured intoUS. Pat.

For example, a fraction which contains dimethylnaphthalenes and boilsmainly in the range of 480-540 F. can be alkylated with a C -Chydrocarbon. The alkylatcd fraction can then be distilled to recover afraction boiling substantially within the range of 480-540 F. (andcontaining a lower proportion of aromatic hydrocarbons than were presentin the charge to the alkylation reactor) and a higher boiling fractionwhich is useful as a plasticizer. The resulting 480-540" F. distillatefraction of the alkylate can then be catalytically hydrogenated in asecond step to produce a second stage hydrogenation product having aluminometer number of at least 75. If, with a particular charge stockand particular alkylation The remaining fractions of this distillationcan be especially useful as a jet fuel or as components of a jet fuelhaving a luminometer number of at least 75.

As an alternative, the aromatic content of a catalytic gas oil (or otherhighly aromatic charge) can be reduced by extraction with an acid (e.g.,H 50 or with an aromatic selective solvent such as phenol or furfural,and the resultant aromatic-depleted product can be utilized as the feedto either the first stage or to the second stage of the above-referredtwo-stage hydrogenation process.

Another alternative open to the refiner is to produce a second stagehydrogenation product which has a luminometer value less than 75, and tothen feed this product to a hydrocracking zone under conditions suchthat the hydrocracked product can be distilled to produce a jet fuelhaving the desired luminometer value.

Another alternative with highly aromatic feeds, such as catalytic gasoil, is to conduct the hydrogenation in at least one stage underconditions such that some hydrocracking occurs (e.g., 10-30 vol. percentconversion to lower boiling products). In such hydrotreating combinedwith hydrocracking, it is preferred that the carrier for thehydrogenation catalyst have some cracking activity (or acidity), such ascan be obtained with an acidic aluminosilicate zeolite which issubstantially free from alkali metals (for example, 10% of Hy zeolite ina silica alumina matrix). Another catalyst which is useful for bothhydrogenating and also for partially hydrocracking (especially in thesecond hydrogenation stage) comprises nickel and tungsten on analumino-silicate carrier (such as the commercially available catalystsold by Harshaw Chemical under the trade name Ni-440l Wherehydrocracking activity is not desired (or is to 'be minimized), asuitable catalyst for deep hydrogenation is Ni-W on A1 0 (such as thecommercially available catalyst from Harshaw Chemical having the tradedesignation Ni-4403). For example, one such type of commercial catalystcontains 7.6 weight percent 'NiO, 23.9 weight percent W0 and theremainder is either A1 0 or an alumino-silicate containing 43% A1 0Another suitable ca-talyst for the second stage is sold under the tradedesignation Filtrol 500-8 and is Ni-Co-Mo on A1 0 In the first stage,the preferred catalysts comprise cobalt and molybdenum oxides on acarrier (such as bauxite or alpha-alumina) or nickel-molybdenum oxideson a carrier. Preferably, these catalysts are presulfided.

When the charge stock which is to be converted into a jet fuel having aluminometer number of at least 75 has a high content of aromatichydrocarbons, such as a 400-550 F. gas oil (or coker distillate from tarsands bitumen), a preferred process is that shown in parent application,Ser. No. 532,298 (now US. Pat. No. 3,424,673) wherein the 400-550 F.charge stock (which can be a catalytic gas oil) is hydrodesulfurized (asin the first stage of the present process) and the hydrodesulfurizedproduct is separated, by distillation, into a fraction boiling below 480F., a fraction boiling above 540 F., and a fraction containingdimethylnaphthalene and boiling mainly in the range of 480-540 F. The480- 540 F. feed fraction is then catalytically hydrogenated to anaromatics content less than 8% under hydrogenation conditions comprisinga temperature in the range of 400-1000 F., a pressure in the range of500-4000 p.s.i.g., a liquid hourly space velocity in the range of 01-100and in the presence of 500-15,000 s.c.f. of hydrogen per barrel ofhydrocarbon feed. The hydrogenated product is distilled t separate afraction containing at least dimethyldecalin and boiling in the range of400-450 F. Most preferably, the first hydrogenation stage is conductedunder conditions such that the first stage hydrodesulfurized productcontains less than 300 p.p.m. (preferably under 50 p.p.m.) of sulfur.All of the material in the 400-550 P. fraction which is the feed to thefirst stage and which is not recovered as dimethyldecalins, can becombined with the desulfurized fraction boiling below 480 F. to producea jet fuel having a luminometer value of at least 75.

ILLUSTRATIVE EXAMPLES A straight-run kerosene meeting the specificationsfor J-P-S and having the properties listed in Table I under the headingcharge, and containing 12.4% aromatics, was hydrodesulfurized in thepresence of a sulfided catalyst comprising cobalt and molybdenum oxideson alumina (which catalyst was commercially available under the tradename Aero HDS-2). The hydrodesulfurization was conducted at 750 p.s.i.g.and 600 F. at a liquid hourly space velocity of 2 and with a hydrogenrecycle of 5,000 set. per barrel of charge. The hydrodesulfurizedproduct was then charged to a second hydrogenation stage wherein thecatalyst was Ni on kieselguhr. The second stage hydrogenation wasconducted at 500 F. and at 500 p.s.i.g., at a liquid hourly spacevelocity of 0.75 with a hydrogen recycle of 10,000 s.c.f./bbl. of feed.The product of the second hydrogenation stage contained only 0.05% byweight of aromatic hydrocarbons and had a smoke number of 35. Otherproperties of this two-stage product, are listed in the table under theheading JP-SA. From the California Research correlation, a smoke numberof 35, for the second stage product, corresponds to a luminometer numberof 82.

Table I also lists, for purposes of comparison, runs pylene tetramerhaving a smoke point can be blended with from 75-65 volume percent ofthe above-described 35 smoke point product from the two stagehydrogenation, to produce a fuel having a high smoke point and lowfreeze point. Such a high smoke point, low freeze point blended fuel canalso be obtained when from 25-35 volume percent of the hydrogenatedtetramer or of ndecane is blended with dearomatized straight runparaffinic kerosene. Such a dearomatized straight run paraffinickerosene can be obtained by 90-100% removal of aromatics from a straightrun kerosene which meets JP-S specifications. The aromatics can beremoved by contacting the kerosene with a strong acid (e.g. H 804), anaromatic selective solvent (e.g. phenol) or an adsorbent (e.g. silicagel, Type Y or Type X faujacite).

A fuel having a freeze point of 69 F. and a smoke point of greater thanwas obtained by blending a completely dearomatized straight runparaflinic kerosene (similar to the charge in Table I) with 23.5 volumepercent of n-decane. A similar blend but with 28.4% dodecane instead ofthe n-decane, produced a blended jet fuel having a 38 smoke point and a22 F. freeze point. Another highly parafiinic fuel which can be usefulper se or as a blending component is obtained by hydrotreating astraight run kerosene (as in the first stage of the two stage processdescribed herein) and then conducting the second stage under reformingconditions (Pt or PtRc catalyst, 775-950 R, 200-600 p.s.i.g., 65-95 molepercent hydrogen in recycle, 4:1 to 10:1 hydrogen to hydrocarbon ratio)and then to dearomatize this second stage product by removal of thearomatics (as with silica gel). This dearomatized reformate can have asmoke point greater than 45. Hydrotreated, reformed, dearomatized fuelsare shown in British Pat. 870,474 published June 14, 1961.

TABLE I.PREPARATION OF JET FUELS Charge stock JP-5 Propylene tetramerOperation Moderate Deep hydrogenation hydrogenation Saturation of ofaromatics oi aromatics olefins 2 stages, (1) CoMo; (2) Ni Catalyst typeCharge Ni-W Ni-W CoMo Charge CoMo Reactor conditions:

Operating pressure, p.s.i.g 750 500 1, 800 750 Gas recycle rate,s.c.i./bbl 5, 000 10, 000 5, 000 0 Temperature F.) 725 500 575 600Liquid hourly space velocity- 2 0. 75 1 1. 5 Inspection data:

Gravity, AP 43. 9 46.3 44. 8 44. 4 Distillation (Engler) F.:

10 393 392 393 388 419 418 418 419 90 465 452 444 449 Aromatics, wt.percent 12. 4 0. 05 4. 0 Olefins, wt. per Freezing point, F.. -54 51 58Flash point (00.), F 154 148 Est. luminometer number 82 69 Smoke point24 35 30 Aniline point, F

1 Desulfurization step. 1 Deep hydrogenation step. Luminometer numberestimated from smoke point.

made on the same straight-run kerosene wherein only a singlehydrogenation (or hydrodesulfurization) stage was used. Also shown, forcomparison purposes, are similar runs made on propylene tetramer (whichis a product obtained by the catalytic polymerization of propylene inthe presence of a phosphoric acid on kieselguhr catalyst). Thehydrogenated propylene tetramer makes an excellent blending stock forincorporating with our two-stage hydrogenation products in order to makeproducts having luminometer values above 85 (surprisingly, suchhydrogenated acyclic olefins can be produced which have luminometervalues of 100).

For example, 25-35 volume percent hydrogenated pro- In the claims:

1. The method of manufacturing a jet fuel, having an ASTM smoke point ofat least 35 mm. which comprises contacting a straight-run paraffinickerosene having a smoke point below 28 and an API gravity of at least 42with hydrogen in the presence of a hydrogenation catalyst formed from atleast one member selected from the group consisting of nickel, cobalt,molybdenum and tungsten and oxides and sulfides thereof, on an inertporous carrier, at a temperature of 500 F. to below 650 F., at apressure of 500 to 1500 p.s.i.g. with a liquid hourly space velocity of1.0 to 6.0 and a hydrogen circulation rate of 1,500 to 10,000 standardcubic feet per barrel of kerosene, contacting the resultant product withhydrogen in the presence of a catalyst which comprises a metal selectedfrom the group consisting of nickel, cobalt, tungsten, molybdenum andthe noble metals, said catalyst being supported on a porous refractorysupport selected from the group consisting of alumina and kieselguhr, ata temperature of 450 to 700 F. at a pressure of 500 to 1500 p.s.i.g., aliquid hourly space velocity of 0.5 to 10.0 and a hydrogen circulationrate of O20,000 standard cubic feet per barrel of said product of thefirst stage, the combination of conditions being selected to produce asuperior jet fuel having a luminometer number of at least 75 and an ASTMsmoke point of at least 29 mm. and blending said superior jet fuel withfrom 15-45 volume percent n-decane.

2. A process comprising substantially reducing the aromatic content of astraight-run paraffinic kerosene containing in the range of 9-16%aromatics to produce a dearomatized kerosene having a smoke pointgreater than 29 and blending the dearomatized kerosene with at least oneC paraffin in an amount etfective to increase the smoke point of saiddearomatized kerosene.

3. A process according to claim 2 wherein said dearomatized kerosene isproduced by hydrogenation of a straight run kerosene having an APIgravity of at least 42 and wherein said paraffin is n-decane.

4. A process according to claim 2 wherein said dearomatized kerosene isproduced by contacting a straight run kerosene having an API gravity ofat least 42 with silica gel.

5. A process of claim 2 wherein said paraflin consists essentially ofn-decane.

6. Process of claim 2 wherein the product of said process has a smokepoint of at least and a freeze point below 20 F.

7. Process of claim 2 wherein said parafi'inie kerosene has a smokepoint below 28.

8. Process of claim 2 wherein said effective amount is in the range of1545 vol. percent.

References Cited UNITED STATES PATENTS 2,910,426 10/1959 Gluesenkamp etal. 20815 3,125,503 3/1964 Kerr et al. 20815 3,146,186 8/1964 Leas et al208-15 3,493,491 2/ 1970 Barnes et al. 20815 3,527,693 9/1970 Barnes etal. 208-15 3,369,998 2/1968 Bercik et al. 208210 3,367,860 2/1968 Barneset al. 208-15 3,436,336 4/ 1969 Ireland 20815 FOREIGN PATENTS 870,4746/1961 Great Britain 20815 HERBERT LEVINE, Primary Examiner US. Cl. X.R.208-15

